1. Field of the Invention
The invention relates to railroads generally, and more particularly to a method and system for identifying problems with train tracks.
2. Discussion of the Background
Track circuits of various types have been used for many years in the railroad industry to determine whether sections or blocks of train track are safe for transit. These track circuits determine such things as whether there is a train in a section of track, whether there is a broken rail in a section of track, whether there has been an avalanche or whether snow or other debris is on the section of track, and whether the section of track is properly aligned with a bridge (with moveable and/or permanent spans). These and other such track circuits will be referred to herein as “track integrity circuits” or simply “track circuits.”
Some known circuits combine the functions of detecting broken rails and detecting trains in a section of track. In their simplest form, these circuits involve applying a voltage across an electrically discontinuous section of rail at one end and measuring the voltage at the other end. If a train is present between the point at which the voltage is applied and the point at which the measuring device is located, the wheels and axle of the train will short the two rails and the voltage at the other end of the track will not be detected. Alternatively, if there is a break in one of the rails between the point at which the voltage is applied and the point at which the voltage measuring device is located, the voltage won't be detected. Thus, if the voltage cannot be detected, there is either a break in the rail or the track is occupied by another train. In either event, it is not safe for a train to enter the section of track monitored by the track circuit.
Many variations of such circuits have been proposed. Examples of such circuits can be found in U.S. Pat. Nos. 6,102,340; 5,743,495; 5,470,034; 5,145,131; 4,886,226; 4,728,063; and 4,306,694. These circuits vary in that some use A.C. signals while other employ D.C. signals. Additionally, some of these circuits employ radio links between the portions of the circuit which apply the signal to the rails and the portions of the circuit that detect the signals. There are yet other differences in these circuits. These differences are not important within the context of the present invention and any of these circuits may be used in connection with the invention.
In traditional systems, the track circuit was connected to a wayside color signal to indicate the status of the track to approaching trains and the track circuit operated continuously or periodically regardless of whether any train was approaching the section of track monitored by the track circuit. There are two major problems with such systems. First, the operation of the track circuit in the absence of an oncoming train wasted power. This limited the use of such systems to locations near a source of power. Second, the use of wayside signals was not failsafe in that it required the conductor/engineer to observe the signal and stop the train when the signals indicated that there was a problem such as a train on the track or a broken rail. Because human beings are not perfect, signals were sometimes missed and accidents resulted.
Some known systems solve the first problem by activating the track detection circuit only when a train is approaching. For example, U.S. Pat. No. 4,886,226 describes activating a broken rail circuit only when an approaching train triggers a “feed” positioned before the section of track monitored by the track circuit. While this solution does conserve power and allow the broken rail detection circuit to be used with a solar cell or battery power source, it has the disadvantage of high maintenance costs associated with the “feed”. Another prior art system described in U.S. Pat. No. 4,728,063 requires a dispatcher to monitor a location of a train and activate a broken rail detection circuit by radio when the train nears the end of the block. The status of the track as reported by the broken rail detection circuit is then transmitted back to the dispatcher, who in turn passes it along by radio to the train. This system is inefficient in that it places an increased processing load on the dispatcher, as the dispatcher is forced to receive and send such messages each time each train reaches a new track circuit. It is also problematic when communications between the dispatcher and the broken rail detection circuit become interrupted.
Approach lit signaling is also know in the art. In those system, the signal lights are only lit when a train approaches the signal. However, in the systems known to the inventors, the track integrity circuit remains on even when the signal lights are out (the main reason the signal lights are turned off is to make the signal lights less attractive to vandals). Furthermore, the track integrity circuits in these systems conserve relatively large amounts of power. These systems are therefore not suitable for use with solar and/or battery power.
What is needed is a method and system for activating track circuits in an economical manner that allows such circuits to be used in a way that minimizes power consumption while avoiding undue burden on a dispatcher or other control authority.